1. Field of the Invention
This invention relates to a printer, and more particularly to a printer such as an electro-thermic printer which has a ribbon cassette mounted in a stationary state independently of the carriage. The ribbon cassette lets off the ink ribbon from the ribbon cassette and recovers it into the ribbon cassette by means of a print head mounted on the carriage along with the reciprocal motion of the carriage in the printing direction.
2. Description of the Related Arts
The conventional printer using an ink ribbon was generally composed so as to mount the ribbon cassette on the carriage together with the print head, but the weight of the entire carriage was increased by mounting the ribbon cassette and ribbon take-up mechanism, and it was hard to move the carriage at high speed. Besides, in order to move this heavy carriage at high speed, a driving motor of a high output torque was required, and in this respect, too, the size of the carriage was enlarged, and the ribbon cassette that could be mounted on the carriage was limited accordingly.
As a means of solving these problems, meanwhile, a new mechanism was proposed in the Japanese Laid-open Patent Publication No. 58-217384. In this printer, structurally, the ribbon cassette is mounted in a stationary state independently of the carriage, and along with the reciprocal motion of the carriage in the printing direction, the ink ribbon is let off from the ribbon cassette by the print head mounted on the carriage, and is recovered into the carriage.
This printer, however, of the ribbon cassette fixed type involves the following technical problems that must be solved. That is, although the carriage can be reduced in size and weight and can be moved at high speed because the ribbon cassette is not mounted on it, but when transferring the ink ribbon, whenever the carriage is returned to the initial printing position (home position), a friction member for pressing and fixing the ink ribbon to the platen at the initial printing position is separated from the platen, and the take-up side reel is rotated in the take-up direction, and the unused ink ribbon for the portion of the length to record while the carriage makes one reciprocal stroke is preliminarily taken up on the take-up side reel. Consequently, the friction member presses and fixes the ink ribbon to the platen by means of a driving source such as magnet to define the let-off of the ink ribbon from the feed side reel, and the carriage moves in the printing direction, and along with this movement, the unused ink ribbon which has been previously taken up is let off from the take-up side reel, and is printed by the print head, and when returning as the carriage reaches the end of the printing direction, the used ink ribbon is taken up by the take-up side reel, and the same operation is repeated.
Thus, since the ink ribbon in the length necessary for one reciprocal stroke of the carriage is preliminarily taken up on the take-up side reel and the initial printing portion of this ink ribbon is fixed by the friction member, if non-printing blank portions occur continuously in the printing process, the print head is released from the ink ribbon, but these portions remain unused, and are taken up on the take-up side reel when returning the carriage. That is, since the action generally known as ribbon skip cannot be effected, the ink ribbon is consumed needlessly. Moreover, since the ink ribbon in the printing length by one reciprocal stroke of the carriage is preliminarily taken up on the take-up reel side whenever the carriage comes to the initial printing position, it is extremely inefficient, and the take-up diameter of the ink ribbons on both reels changes every moment as the ink ribbon is taken up from the feed side reel to the take-up side reel, so that the rotation control of the motor for taking up the ink ribbon preliminarily on the take-up side reel is very difficult.
In such a printer of the ribbon cassette fixed type as described above, the carriage moves while the cassette is fixed while other functions are to be achieved as a printer. This structure is rather complicated compared with the printer of the ribbon cassette moving type. Consequently, the cassette loading operation, in which the ribbon is to be properly set to the carriage in such a structure, tends to be also complicated. In such a printer of the ribbon cassette fixed type, on one hand, the carriage and the cassette are better to be positioned closer to each other for easily setting the ribbon to the carriage generally in its loading operation, but on the other hand, the cassette can not be positioned so close to the carriage as to disturb the movement of the carriage in its printing operation.